GALCIT Colloquium

The talk will be on the development of experimental measurement and data-processing methodologies based on planar laser-induced fluorescence (PLIF) and other diagnostic techniques, in collaboration with Daniel Lang. The experiments investigated the downstream transport, dispersion, diffusion, and mixing of a miscible passive scalar from a point-release in grid-turbulence at high Schmidt number. The scalar plumes developed downstream in uniform-density (unstratified) turbulent flow formed by a grid towed in a tank through otherwise stationary water. PLIF image data were processed to calibrate and correct for local variations in gains and offsets over pixels of a custom-designed and fabricated charged-coupled device (CCD) focal-plane image sensor. Data were acquired using illumination from a quad-head pulsed Nd:YAG laser, at pulse rates up to 200 Hz, and recorded by means of a custom-designed and built data-acquisition system. The optical system generated and imaged laser-sheet 2-D streamwise transects, individual 2-D transverse transects, or 2-D transverse transects swept in a direction perpendicular to their plane. Concentration data were processed to extract quantitative flow and scalar-field visualization, and quantitative turbulent-plume statistics, such as mean plume profiles, spatial transverse radial and streamwise scalar spectra, and other information, over a range of mesh Reynolds numbers and downstream distances from the grid, with variable scalar-injection-speed to flow-speed ratios. Preliminary processed sample data illustrate the application of the experimental method and the resulting measurement dynamic range, as required to discern far-field downstream behavior of the scalar plume.